Much attention has been devoted in the past to the reproduction of the gustative notes which typically define the bitter character of certain foodstuffs. In the flavour industry there is in fact a need to provide flavouring ingredients, or compositions thereof, for improving the flavours of beverages or solid foodstuffs, particularly those comprising cocoa or a cocoa imitating substitute, by imparting to said products the distinct bitterness which characterizes the natural cocoa products. Sofar, however, no satisfactory solution has been found to this problem.
The term "bitterness", deemed used in the course of the present description, is deemed to define the gustative property possessed by a given substance of developing a bitter taste.
Most of these substances find their origin in the vegetable kingdom and they often occur in a variety of plants, such as those belonging to the families of Gentianaceae, Compositae and Labiates. Equally, some foodstuffs having a base of animal origin possess a bitter taste when subjected to certain treatments.
The properly so called "bitter substances" do not include however the alkaloid derivatives of purine, whose bitter taste is very often viewed as a side effect [K. Herrmann, Deutsche Lebensmittel Rundschau, 68, 105(1972)].
Most of the bitter substances known hitherto belong either to the class of terpenoids possessing a lactonic or ketonic functional group or to that of phenol derivatives, such as for instance the compounds of the flavanone series found in citrus fruits. Peptides possessing a bitter taste are also known and their organoleptic properties are described in several scientific publications, viz. Zeit. fur Lebensmittel-Untersuch. Forsch., 147, 64 (1971); idem, 149, 321 (1972); Agr. Biol. Chem., 34, 729 (1970); J. Food Sci., 35, 215 (1970).
Certain amino acids [see e.g.: Greenstein and Winitz, Chemistry of the Aminoacids, vol. I, J. Wiley (1961) p. 150] as well as certain oligopeptides [Annual Meeting of the Agr. Chem. Soc. Japan, 42 (1972)] develop bitter gustative notes.
In the course of the past few years, several theories have been advanced in order to better define the relationships which may exist between the chemical structure of a given substance and its developed bitterness [see: Nature, 223, 97-9(1969)]. However, it has to be clearly stated that in the present state of our knowledge, it is impossible to predict the organoleptic properties of a compound on the sole base of its chemical structure. Not surprisingly therefore one may observe that the discovery of new flavouring ingredients, in particular of bitter flavouring ingredients, occurs very often in a pure accidental way.